This is an ESC I also use, watercooled, and it is quite ok... and very cheap:
http://www.himodel.com/electric/HiMo...-70A_OPTO.html
BUT you need an external BEC:
http://www.hobbycity.com/hobbycity/s...oise_Reduction
Can you post some pics of the boat? Especially insides... damfurst got me worried about space...